Electronically scanning antennas comprise a primary source and a network of phase shifters associated with radiating means. Each phase shifter of the type here considered is formed by a microwave line coupled to conventional PIN diodes which, as a function of their conducting or non-conducting state, enable reactances to be introduced which vary the phase angle. The switching from the non-conducting to the conducting state of the dephasing diodes occurs quickly enough. On the other hand, the reverse switching from the conducting to the non-conducting state does not occur instantaneously. At the instant of switching, each diode begins to act as a short-circuit in which a significant reverse current flows before the diode actually cuts off. At the instant, when the polarity of the voltage applied to the junction of each PIN diode is reversed, the current in the diode decreases rapidly and then reverses suddenly. This current is due to the movement of the minority carriers which had previously been accumulated during the period of forward conduction at the junction level.
The charges stored are a function of the lifetime of the minority carriers and of the forward current before switching. The sweep-out of these charges is ensured by quenching or cut-off means which provide a reverse current that produces the elimination of the charge carriers. The quenching operation must be done quickly so that the time required for switching is as short as possible. This condition is indispensable if it is desired to use the phase shifter mentioned above for the antennas of short-range and hence high-repetition-rate radars or for antennas of long-range radars in which it is useful to be able to change the aim of the antenna during a repetition period.
However, the speed of the change of beam orientation is a function of the speed of switching of the dephasing diodes which is in turn related to the intensity of the current supplied by the cut-off means employed.
In accordance with known practice, the means designed to deliver a reverse current as soon as it is desired to cut off the diodes include a high-voltage source combined with a high resistance. The high-voltage supply, which is bulky, operates at high power and with considerable thermal dissipation. As a result, there are large temperature variations in the diode cut-off device and the minority carriers in the dephasing diodes, which have a life that increases with temperature, are eliminated slowly and hence slow down the switching.